Nonapeptide thymic hormone thymulin is produced by thymic endocrine epithelial cells. Its biological activities have been well described and its role in various immunopathological status including AIDS has been implicated. Although its complete amino acid sequence has been established more than 10 years ago, the presence of prothymulin was not discovered till recently. Moreover, its gene has not been cloned yet. The advancement in the field of molecular biology of thymulin has been severely hindered by the lack of in vitro model system. Here we report the recent establishment of thymic endocrine epithelial cell line which produces thymulin and proposes to: 1) purify and sequence prothymulin; 2) clone thymulin gene and 3) study the control mechanism of thymulin gene activation and expression. We are now developing cDNA library from thymic endocrine epithetial cell line. We have also developed rabbit antibody to thymulin which recognizes prothymulin molecule as well. With this cell line and antiserum in our hand, we are confident that we can achieve the proposed study.